Can I call a constructor from another constructor (do constructor chaining) in C++?

Question

As a C# developer I\'m used to running through constructors:

class Test {
    public Test() {
        DoSomething();         


        

Answer 1

In Visual C++ you can also use this notation inside constructor: this->Classname::Classname(parameters of another constructor). See an example below:

class Vertex
{
 private:
  int x, y;
 public:
  Vertex(int xCoo, int yCoo): x(xCoo), y(yCoo) {}
  Vertex()
  {
   this->Vertex::Vertex(-1, -1);
  }
};

I don't know whether it works somewhere else, I only tested it in Visual C++ 2003 and 2008. You may also call several constructors this way, I suppose, just like in Java and C#.

P.S.: Frankly, I was surprised that this was not mentioned earlier.

Answer 2

When calling a constructor it actually allocates memory, either from the stack or from the heap. So calling a constructor in another constructor creates a local copy. So we are modifying another object, not the one we are focusing on.

Answer 3

Another option that has not been shown yet is to split your class into two, wrapping a lightweight interface class around your original class in order to achieve the effect you are looking for:

class Test_Base {
    public Test_Base() {
        DoSomething();
    }
};

class Test : public Test_Base {
    public Test() : Test_Base() {
    }

    public Test(int count) : Test_Base() {
        DoSomethingWithCount(count);
    }
};

This could get messy if you have many constructors that must call their "next level up" counterpart, but for a handful of constructors, it should be workable.